What is global warming?

Global warming - Wikipedia, the free encyclopedia

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** Global warming **

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This article is about the current change in Earth's climate. For general
discussion of how the climate can change, see Climate change. For other
uses, see Global warming (disambiguation).
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refer to caption
Global mean land-ocean temperature change from 1880â2012, relative to
the 1951â1980 mean. The black line is the annual mean and the red line
is the 5-year running mean. The green bars show uncertainty estimates.
Source: NASA GISS. (/click for larger image/)
Map of temperature changes across the world
key to above map of temperature changes
The map shows the 10-year average (2000â2009) global mean temperature
anomaly relative to the 1951â1980 mean. The largest temperature
increases are in the Arctic and the Antarctic Peninsula. Source: NASA Earth
Observatory^[1]
refer to caption
Fossil fuel related CO[2] emissions compared to five of the IPCC's "SRES"
emissions scenarios. The dips are related to global recessions. Image
source: Skeptical Science.

*Global warming* is the rise in the average temperature of Earth's
atmosphere and oceans since the late 19th century and its projected
continuation. Since the early 20th century, Earth's mean surface
temperature has increased by about 0.8 Â°C (1.4 Â°F), with about
two-thirds of the increase occurring since 1980.^[2] Warming of the climate
system is unequivocal, and scientists are more than 90% certain that it is
primarily caused by increasing concentrations of greenhouse gases produced
by human activities such as the burning of fossil fuels and
deforestation.^[3]^[4]^[5]^[6] These findings are recognized by the
national science academies of all major industrialized nations.^[7]^[A]

Climate model projections were summarized in the 2007 Fourth Assessment
Report (AR4) by the Intergovernmental